Volatile organic constituents (VOCs), such as methylene chloride, 1,1-dichloroethylene, 1,1-dichloroethane, trans-1,2-dichloroethylene, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,2-dichloropropane, trichloroethylene, tetrachloroethylene, benzene, ethylbenzene, toluene, xylenes and the like are present in soil gas and ground water at various locations throughout the world. Removal of VOCs from gas streams is an important objective of many soil and groundwater remediation programs.
Carbon adsorption techniques for removing chemicals of interest, such as VOCs, from gaseous and vaporous process streams are most efficient when the feed stream is characterized by low relative humidity and moderate temperature. For example, carbon adsorption techniques are generally most effective when input gas streams are at temperatures of less than about 60.degree. C. and more than about 20.degree. C. Moreover, gas streams having a relative humidity in excess of 25% are generally not suitable for processing that involves carbon adsorption techniques, because the carbon may become loaded with water vapor rather than the chemicals of interest.
Obviously, all process streams that might be treated using carbon adsorption do not exhibit the above described temperature and relative humidity characteristics. Conventional soil gas extraction systems employing fans, for example, generally produce a saturated input gas stream at a temperature ranging from about 7.degree. C. to about 13.degree. C. Carbon adsorption is generally not effective to remove chemicals of interest, such as VOCs, from such gas streams. It would be advantageous, therefore, to provide methods and systems for removing VOCs and other contaminants from contaminated gas streams, such as soil gas streams, using carbon adsorption techniques.